While conventional brush-commutated DC motors may have advantageous characteristics, including convenience of changing operational speeds, there may be disadvantages such as brush wear, electrical loss, noise and radio frequency interference caused by sparking between the brushes and the segmented commutator, which may limit the applicability of such brush-commutated DC motors in some applications. Electronically commutated motors, such as brushless DC motors and permanent magnet motors with electronic commutation, have now been developed and generally are believed to have the above-discussed advantageous characteristics of the brush-commutated DC motors without many of the disadvantages thereof while also having other important advantages. Such electronically commutated motors are discussed in the David M. Erdman U.S. Pat. Nos. 4,015,182 and 4,459,519, for instance. In these patents, a brushless DC motor has a stator with a plurality of windings therein, a rotor having a plurality of constant magnetic polar regions, and means for sensing the relative position of the rotor polar regions with respect to the stator. Positive signals developed by the position sensing means were processed by circuitry for selectively energizing the windings of the motor. These electronically commutated motors are advantageously employed in many different applications, for instance, in air handling systems including a fan for either operating the fan to blow air over cooling coils or to blow cooled air from an air conditioner or warmed air from a furnace into ductwork to be circulated in a building.
The control circuitry required to electronically commutate a brushless DC motor in air handling systems is typically mounted remote from the motor in a location where the circuitry can be adequately cooled and unaffected by motor heat. This arrangement requires additional space for the control circuitry and a cable for connecting the control circuitry to the motor. The cable connecting the control circuitry to the motor emits radio frequency (RF) signals which may interfere with other electrical equipment located near the motor.
In applications where the control circuitry is mounted in proximity to the motor, a dedicated cooling mechanism such as a fan wheel is generally employed to provide the required heat dissipation, i.e., the mechanism is provided primarily for the purpose of cooling the control circuitry. However, the dedicated cooling mechanism results in additional cost and failure of such mechanism results in added maintenance expenses.
Further improvements in control systems, electronically commutated motor systems, and methods of control and operation can beneficially contribute to more widespread use of such motors in air handling systems. Improvements which achieve increased electrical efficiency and user convenience would be desirable. For example, it would be desirable to both reduce the length of the cable connecting the control circuitry to the motor and mount the control circuitry in proximity to the motor in a configuration which would not require a dedicated cooling mechanism.